Atherosclerosis, the leading cause of death in the United States, is currently addressed through several treatment modalities, including angioplasty, endarterectomy, and bypass. When a vessel is injured during angioplasty or bypass graft surgery, the injury can induce a physiological response that becomes evident 3-6 months later whereby the vessels are further narrowed (“restenosis”). Restenosis involves (i) intimal cell hyperplasia (growth of inner vessel lining), and (ii) constrictive vessel wall remodeling. Neo-intimal thickening can be accompanied by compensatory enlargement of the vessel wall, which can be measured by changes in external elastic lamina area. This growth, termed adaptive remodeling, which prevents the neo-intimal lesion from impinging on the lumen, is triggered by the activation of smooth muscle cells (SMCs) lining the arterial walls. Restenosis occurs in 30-50% of the 2 million patients who undergo this surgery every year.
Currently, restenosis is treated by rapamycin provided through stents. Unfortunately, stents increase fibrosis and intima thickening and do not allow vessels to expand. Stents also prevent healing of the endothelial layer, causing thrombosis. Rapamycin interferes with re-endothelization, which is required for proper vessel healing. Further, rapamycin provided via stent is susceptible to rapid dilution by the bloodstream. Systemic treatments, which cannot be targeted to the site of restenosis, are generally very limited.
Vessel walls are primarily composed of collagen types I (rigid) and III (elastic). Connective Tissue Growth Factor (CTGF), a soluble factor secreted by blood vessel adventitial cells, activates smooth muscle in the vessel causing increased adaptive remodeling of the vessel (Kundi et al., Cardiovascular Research 84:326-335, 2009). In a laboratory model of restenosis, the lumen of balloon-injured blood vessels was expansively remodeled when CTGF was applied (Kundi et al., 2009). However, CTGF alone is not sufficient to treat restenosis, at least because it neither suppresses neo-intimal growth nor vessel constriction.
CTGF induces collagen synthesis (see U.S. Patent Publication No. 2003/0180300). The combination of insulin (10 ng/ml) and CTGF (2.5 ng/ml) stimulates total collagen synthesis in dermal fibroblasts isolated from patients with scleroderma/systemic sclerosis (Gore-Hyer et al., Arthritis and Rheumatism 48:798-806, 2003). Normal rat kidney (NRK) fibroblasts stimulated with TGFbeta or CTGF in the presence of IGF-2 responded by differentiating into myofibroblasts and increasing both collagen type I and collagen type III synthesis, with no indication that collagen III levels increased significantly relative to collagen I levels (Grotendorst et al., FASEB 18:469-479, 2004). Further, the combination of CTGF and IGF-2 had no significant effect on cell proliferation or collagen synthesis in human Tenon's fibroblasts (Seher et al., Mol. Vision 17:53-62, 2011).
Previous work suggests that insulin can be used to increase re-endothelialization in vessels and to inhibit cell migration into the intima (Breen et al., Arterioscler. Thromb. Vasc. Biol. 29:1060-1066, 2009). However, insulin does not decrease intima cell proliferation or apoptosis (Breen, et al., 2009), and evidence suggests that insulin stimulates adaptive remodeling of injured vessels.
There has arisen in the art a need for an anti-restenosis agent. Preferably, an anti-restenosis agent could preserve vessel lumen size by suppressing both neo-intimal growth and vessel constriction and also enhance adaptive remodeling in injured vessels.